A conventional punch and die set for punching holes in strip metal comprises a die assembly having a facial surface and having a die opening extending into the facial surface. The punch assembly, which is opposed to the die assembly, has a punch projecting therefrom which is dimensioned to enter the die opening so that when strip material is located between the punch and die and the punch and die are moved towards each other, a hole will be formed in the strip by the punch. The slug or scrap metal produced when the hole is formed is pushed by the leading end of the punch into the die opening and removed in any suitable manner.
After a die assembly has been in use for some time, the edges of the die opening at the facial surface of the die assembly become worn and the holes which are produced in the strip metal by the punch and die will not have the dimensional precision which may be required in the part that is being produced. It is therefore common practice to sharpen the die, a process which is carried out by grinding the surface of the die assembly so that the surface material is removed and the dimensional precision of the die opening is restored. A conventional die assembly has a die plate in which many die openings are provided. In order to avoid the necessity of grinding the surface of the die plate, it is common practice to provide die inserts in the die plate which have the die openings therein. The inserts are mounted in a recess in the die plate and held in position by a laterally extending projection on the insert which is received in a die backup block, or spacer, of the die assembly so that when the die plate is secured to the spacer or die backup block, the insert will be securely held in the recess in the die plate. Where die inserts are used, sharpening of a particular insert can be carried out by removing that insert from the die assembly and sharpening only that particular insert. The sharpening process, however, is time consuming and requires the services of a highly skilled machinist for the reason that when the surface of the insert is ground during a sharpening process, the thickness of the insert is thereby reduced and it is necessary to place a suitable shim beneath the insert so that the surface of the insert will be coplanar with the facial surface of the die plate. This means that the laterally extending ear or retaining portion of the insert must also be ground in a precision grinding operation. The advantages of using die inserts are, to some extent at least, nullified by the difficulty of sharpening a die insert.
The present invention is directed to the achievement of an improved die insert by means of which the necessity of sharpening the insert is eliminated and, at the same time, the useful life of the insert is extended. The invention is further directed to the achievement of an improved method of manufacturing die insert and improved methods of mounting die inserts in a die assembly.